1mm/1.5mm clips will be too small for 3 core. Use 2.5mm clips or buy the ones specifically for 3 core. 2.5mm will work ok but cable will be a loose fit so your cable will flop about a bit. If it's on display I would use conduit or chase and plaster in.

You should always purchase the correct size clips for the cable Tower being my brand of preference..nowt worse then seeing oversized clips being used - aye one example being the use of 2.5 clips on 1mm cable, its not professional and it looks pants..and also white clips on grey cable really is so naff..grey for grey cable and white for white cable, although myself I never use white t + e